Nonwoven materials are known to be suitable for producing many types of limited use or disposable protective garments such as surgical gowns, industrial work wear, coveralls, as well as cover materials for disposable personal care products such as disposable diapers and incontinence garments. The usefulness of such garments is influenced by factors such as comfort and resistance to liquids.
Factors affecting the comfort of someone wearing such garments include the stretch properties, softness and breathability of the garment material. Materials that are soft, stretchable and breathable are typically more comfortable than materials that do not have those characteristics. Stretchable materials may be classified into two broad categories: materials having "recoverable stretch" and materials having "non-recoverable stretch." A material can be described as having recoverable stretch if it contracts upon termination of a biasing force following stretching of the material by application of the biasing force. Material having non-recoverable stretch does not contract in this manner. In most situations, material having recoverable stretch is more desirable for protective garments than material having non-recoverable stretch, especially in environments where baggy or loose fitting garments may snag and tear to reduce the protection of the wearer or become caught in machinery.
In the past, recoverable stretch properties have been incorporated into garments by use of elastomeric sections, pieces and/or strips such as, for example, elastomeric nonwoven webs formed from A-B-A' block copolymers, polyurethane elastomeric materials, polyamide elastomeric materials, polyester elastomeric materials, and elastic copolymers of ethylene and at least one vinyl monomer such as, for example, vinyl acetates, unsaturated aliphatic monocarboxylic acids, and esters of such monocarboxylic acids. Although such extrudable elastomeric materials provide highly desirable stretch, they are relatively expensive and, in some cases, may break down if exposed to certain liquids and/or gases that can be present in many industrial and medical environments. Furthermore, a process of manufacturing garments by joining several different fabrics together generally tends to be more complex and less efficient than a process of making garments from a single fabric. Complex and relatively inefficient manufacturing processes generally reduce the cost advantages provided by inexpensive materials.
A material that has recoverable stretch without using the elastomeric materials described above has been suggested in U.S. Pat. No. 4,965,122. According to that patent, a tensioning force is applied to a fabric to reduce its width. Such a tensioned or drawn material is referred to as a "necked" material. That material is heated and cooled while it is necked so that it retains a memory of its necked condition which causes it to recover to generally about its necked dimensions after non-destructive stretching. For example, U.S. Pat. No. 4,965,122 teaches that a reversibly necked material may be adapted to stretch at least about 75 percent and recover at least 50 percent when stretched 75 percent.
Protective garments should also be resistant to liquids. For example, surgical gowns, drapes, face masks, shoe covers and the like must be relatively resistant to liquids. For a variety of reasons, it is undesirable for liquids and/or pathogens which may be carried by liquids to pass through a surgical gown or patient drape to contact medical personnel or patients.
Similarly, it is often highly desirable to isolate persons from harmful substances which may be present in a work place or accident site. To reduce the chance of exposure, workers would benefit from wearing protective clothing that is relatively liquid resistant but which is still comfortable so it does not reduce their performance. In the case of personal care products, such as diapers and adult incontinence products, it is desirable to provide a garment which is comfortable and which resists leakage of liquids. In all such products, it is also highly desirable that the product be inexpensive so as to be disposable.
It is highly desirable to have a garment made of a material that allows air and water vapor to pass but which is still relatively resistant to the passage of liquids. A "breathable" material can increase the comfort of someone wearing a garment, especially if the garment must be worn under high heat index conditions, during vigorous physical activity, or for long periods. Ventilation holes, ports and/or panels may be relatively ineffective and may compromise the protection of the wearer. Furthermore, a process of manufacturing garments with ventilation holes, ports and/or panels generally tends to be more complex and less efficient than a process of making garments without such features. Complex and relatively inefficient manufacturing processes generally reduce the cost advantages provided by inexpensive materials.
Many attempts have been made to provide protective garments which are breathable, relatively liquid impervious, have recoverable stretch and are so inexpensive that they can be discarded after only a single use. One problem that has been encountered is that inexpensive materials which might be used for such garments generally have poor resistance to liquids, poor stretch recovery, and low levels of breathability.
Certain inexpensive, liquid resistant materials are known. An exemplary material is a calendered flash-spun polyethylene spunbond material known in the art as Tyvek.RTM., available from E. I. DuPont De Nemours. Although Tyvek.RTM. is an inexpensive, strong, liquid resistant material it offers little breathability or stretch. Another exemplary material is generally known in the art as spunlace fabric. For example, spunlace fabric may be obtained from E. I. DuPont De Nemours under the trade designation Sontara.RTM.. Although spunlace fabric is inexpensive, breathable, stretchable, and liquid resistant, it generally exhibit non-recoverable stretch. Garments made of such inexpensive materials often require other materials, components, treatments, or the like to provide comfort features such as, for example, conformability, breathability or recoverable stretch that are lacking in a garment composed only of the inexpensive material.
Thus, a need exists for protective garments that requires little or no other materials, components, treatments, or the like to provide desirable comfort features such as, for example, conformability, breathability, liquid resistance, or recoverable stretch. For example, a need exists for protective garments that are composed substantially or entirely of an inexpensive material such that the garments are liquid resistant and so inexpensive as to be disposable while also being conformable, breathable, and having recoverable stretch.
Definitions
As used herein, the term "recoverable stretch" refers to the difference between the stretched dimension of a material following the application of a biasing force and that same dimension upon termination of the biasing force. Percent recoverable stretch may be expressed as [(maximum stretch length-recovered sample length)/recovered sample length].times.100. For example, if a material having a stretched or extended length of 1.85 inches contracts, that is, recovers 0.85 inch to a length of 1 inch, that material can be said to have a recoverable stretch of 85 percent.
As used herein, the term "non-recoverable stretch" refers to elongation of a material upon application of a biasing force which is not followed by a contraction of the material as described above for "recoverable stretch". Non-recoverable stretch may be expressed as follows:
Non-recoverable stretch=100-recovery when the recovery (defined below) is expressed in percent.
As used herein, the term "recovery" refers to the contraction of a stretched material upon termination of a biasing force following stretching of the material by application of the biasing force. For example, if a material having a relaxed, unbiased length of one (1) inch is elongated 50 percent by stretching to a length of one-and-one-half (1.5) inches, the material is elongated 50 percent (0.5 inch) and has a stretched length that is 150 percent of its relaxed length. If this stretched material contracts, that is, recovers to a length of one-and-one-tenth (1.1) inches after release of the biasing and stretching force, the material has recovered 80 percent (0.4 inch) of its one-half (0.5) inch elongation. Percent recovery may be expressed as [(maximum stretch length final sample length)/(maximum stretch length-initial sample length)].times.100.
As used herein, the term "nonwoven web" refers to a web that has a structure of individual fibers or filaments which are interlaid, but not in an identifiable repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes known to those skilled in the art such as, for example, meltblowing and melt spinning processes, spunbonding processes and bonded carded web processes.
As used herein, the term "spunbonded web" refers to web of small diameter fibers and/or filaments which are formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries in a spinnerette with the diameter of the extruded filaments then being rapidly reduced, for example, by non-eductive or eductive fluid-drawing or other well known spunbonding mechanisms. The production of spunbonded nonwoven webs is illustrated in patents such as Appel, et al., U.S. Pat. No. 4,340,563; Dorschner et al., U.S. Pat. No. 3,692,618; Kinney, U.S. Pat. Nos. 3,338,992 and 3,341,394; Levy, U.S. Pat. No. 3,276,944; Peterson, U.S. Pat. No. 3,502,538; Hartman, U.S. Pat. No. 3,502,763; Dobo et al., U.S. Pat. No. 3,542,615; and Harmon, Canadian Patent No. 803,714.
As used herein, the term "meltblown fibers" means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into a high-velocity gas (e.g. air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameters, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high-velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. The meltblown process is well-known and is described in various patents and publications, including NRL Report 4364, "Manufacture of Super-Fine organic Fibers" by V. A. Wendt, E. L. Boone, and C. D. Fluharty; NRL Report 5265, "An Improved device for the Formation of Super-Fine Thermoplastic Fibers" by K. D. Lawrence, R. T. Lukas, and J. A. Young; and U.S. Pat. No. 3,849,241, issued Nov. 19, 1974, to Buntin, et al.
As used herein, the term "microfibers" means small diameter fibers having an average diameter not greater than about 100 microns, for example, having a diameter of from about 0.5 microns to about 50 microns, more specifically microfibers may also have an average diameter of from about 4 microns to about 40 microns.
As used herein, the term "disposable" is not limited to single use or limited use articles but also refers to articles that are so inexpensive to the consumer that they can be discarded if they become soiled or otherwise unusable after only one or a few uses.
As used herein, the term "garment" refers to protective garments and/or shields including for example, but not limited to, surgical gowns, patient drapes, face masks, shoe covers, diaper outer covers, training pants, coveralls, work suits, aprons and the like.
As used herein, the term "liquid resistant" refers to material having a hydrostatic head of at least about 25 centimeters as determined in accordance with the standard hydrostatic pressure test AATCCTM No. 127-1977 with the following exceptions: (1) The samples are larger than usual and are mounted in a stretching frame that clamps onto the cross-machine direction ends of the sample, such that the samples may be tested under a variety of stretch conditions (e.g., 10%, 20%, 30%, 40% stretch); and (2) The samples are supported underneath by a wire mesh to prevent the sample from sagging under the weight of the column of water.
As used herein, the term "stretchably conformable" refers to material having both measurable softness and recoverable stretch. A stretchably conformable material has softness characterized by a drape stiffness in at least one direction of less than about 2.75 cm. For example, a conformable material may have a drape stiffness in at least one direction from less than about 1.5 up to about 2.75 cm. Drape stiffness is determined using a stiffness tester available from Testing Machines, Amityville, Long Island, N.Y. 11701. Test results are obtained in accordance with ASTM standard test D1388-64 using the method described under Option A (Cantilever Test). A conformable material may have measurable softness which is characterized by cup crush test results of less than about 200 grams. For example, a conformable material may have cup crush test results from less than about 150 up to about 200 grams. The cup crush test evaluates fabric stiffness by measuring the peak load required for a 4.5 cm diameter hemispherically shaped foot to crush a 9".times.9" piece of fabric shaped into an approximately 6.5 cm diameter by 6.5 cm tall inverted cup while the cup shaped fabric is surrounded by an approximately 6.5 cm diameter cylinder to maintain a uniform deformation of the cup shaped fabric. The foot and the cup are aligned to avoid contact between the cup walls and the foot which might affect the peak load. The peak load is measured while the foot descends at a rate of about 0.25 inches per second (15 inches per minute) utilizing a Model FTD-G-500 load cell (500 gram range) available from the Schaevitz Company, Tennsauken, N.J.
As used herein, the term "breathable" refers to material having a Frazier porosity of at least about 25 cubic feet per minute per square foot (cfm/ft.sup.2). For example, the Frazier porosity of a breathable material may be from about 25 to more than 45 cfm/ft.sup.2. The Frazier porosity is determined utilizing a Frazier Air Permeability Tester available from the Frazier Precision Instrument Company. The Frazier porosity is measured in accordance with Federal Test Method 5450, Standard No. 191A, except that the sample size is 8".times.8" instead of 7".times.7".
As used herein, the term "necked material" refers to any material which has been constricted in at least one dimension by processes such as, for example, drawing.
As used herein, the term "neckable material" means any material which can be necked.
As used herein, the term "reversibly-necked material" refers to a necked material that has been treated while necked to impart memory to the material so that when force is applied to extend the material to its pre-necked dimensions, the necked and treated portions will generally recover to their necked dimensions upon termination of the force. A reversibly-necked material may include more than one layer. For example, multiple layers of spunbonded web, multiple layers of meltblown web, multiple layers of bonded carded web or any other suitable combination of mixtures thereof. The production of reversibly-necked materials is illustrated in patents such as, for example, Mormon, U.S. Pat. Nos. 4,965,122 and 4,981,747.
As used herein, the term "stretch direction" refers to the direction in which a reversibly-necked material has recoverable stretch (i.e., the direction of stretch and recovery).
As used herein, the term "percent neck down" refers to the ratio determined by measuring the difference between the pre-necked dimension and the necked dimension of a neckable material and then dividing that difference by the pre-necked dimension of the neckable material.
As used herein, the term "percent stretch" refers to the ratio determined by measuring the change in the necked dimension of a reversibly-necked material upon application of a stretching force and dividing that value by the necked dimension before application of the stretching force. For example, the percent stretched may be represented by the following expression: EQU % stretch=[(maximum stretched dimension-initial necked dimension)/initial necked dimension].times.100
As used herein, the term "consisting essentially of" does not exclude the presence of additional materials which do not significantly affect the desired characteristics of a given composition or product. Exemplary materials of this sort would include, without limitation, pigments, antioxidants, stabilizers, surfactants, waxes, flow promoters, particulates or materials added to enhance processability of a composition.